Semiconductor components such as CPUs (MPUs) that consume a large amount of electric power also emit a large amount of heat during operation. In order to dissipate heat from the semiconductor components, a heat sink joined to the upper surfaces of the components has been used to remove (dissipate) heat. The effect of heat dissipation (cooling) can be increased by increasing the size of the heat sink. However, if the size of the whole circuit module is limited, it is often difficult to provide a large heat sink. This trend is being intensified by downsizings of circuit modules.
Semiconductor components are attached to a circuit board by soldering or the like. In that case, because the circuit board contains an insulating material, the thermal conductivity of the circuit board is so low that heat can hardly be dissipated through the circuit board. A fan is provided in a circuit module in order to facilitate heat dissipation from the heat sink. The cooling effect increases as airflow (the number of rotations) of the fan is increased. However, increasing the number of rotations of the fan poses the problem that noise of the fan also increases. Therefore, it is becoming increasingly important to find ways to increase the effect of cooling semiconductor components on circuit boards with the limited size of a heat sink and airflow of a fan.